Method for installing a conductor casing through a suction substructure

ABSTRACT

A suction substructure ( 2 ) is for the setting of one or more conductor casing strings ( 14 ) in connection with drilling of at least one underwater well, preferably a petroleum well. Use of the suction substructure ( 2 ) renders possible the installation of conductor casing by means of known piling technique and by means of a suitable surface vessel, e.g. a suitable boat. The suction substructure ( 2 ) consists of a substructure body, which is joined in a pressure sealing manner, and which is shaped with a downwards open end part ( 8 ), which is set some way down in the seabed sediments ( 22 ). Thereupon water is pumped out of the suction substructure ( 2 ), which causes a negative pressure in the suction substructure ( 2 ), and where the suction substructure ( 2 ) thereby is pressed further down into the seabed sediments ( 2 ). The suction substructure ( 2 ) is in addition in its upper end fitted with at least one guide opening ( 10 ) and possibly an appurtenant guide funnel ( 12 ), and an appurtenant releasable and pressure sealing lid ( 32 ), and where the guide funnel ( 12 ) will be able to guide and give lateral support to a conductor casing string ( 14 ) during its subsequent installation.

CROSS REFERENCE TO RELATED APPLICATION

The present application is the U.S. national stage application ofInternational Application PCT/N001/00062, filed Feb. 21, 2001, whichinternational application was published on Sep. 7, 2001 as InternationalPublication WO 01/65050. The International Application claims priorityof Norwegian Patent Application 20001031, filed Feb. 29, 2000.

FIELD OF THE INVENTION

The invention concerns a substructure device in the shape of a suctionsubstructure and a method for installing it on and in a waterbed as wellas use of the suction substructure in connection with installation ofconductor casing for one or more wells, preferably petroleum well(s), inwhich the installation of suction substructure and drilling of wells areperformed from e.g. a floating installation.

BACKGROUND OF THE INVENTION

The background of the invention is the disadvantages of installation andcosts often experienced with the use of known substructure devices inconnection with the drilling of underwater wells.

KNOWN TECHNIQUE

In connection with known technique the work with a new well is normallystarted by the drilling of a pilot hole from a drilling installation,e.g. a drilling rig, the hole having a diameter of e.g. 36″, down to asuitable depth under the waterbed, typically approx. 70 metres. In thedescription that follows the waterbed will be referred to as the seabed,even if the above seabed may equally well be the bottom of e.g. a lake,a river, a delta or a swamp area.

After the drilling of the above pilot hole the drilling tools and thedrill string are pulled out of the pilot hole. A string composed ofseveral connected conductor casings, i.e. a conductor casing string, isthereupon lowered down into the pilot hole by means of an installationstring of drill pipes connected to the conductor casing string. Thenfloating cement (cement grout) is pumped down through and out of thebottom of the installation string and the conductor casing string, sothat the cement grout is displaced up into the tubular space between thepilot hole and the conductor casing string. The conductor casing stringmust then be held in a preferably vertical position until the cementgrout is sufficiently hardened, and thus has achieved a load carryingstrength, which is sufficient for supplying the conductor casing stringwith necessary lateral support during later strains.

To facilitate the installation of the conductor casing, a guide base isconnected to the conductor casing string's upper end. Seen from abovethe guide base normally has a rectangular shape, and each of the fourcorners of the guide base is fitted with a guide post with the objectiveof being an anchoring point for an appurtenant guide line. Each of thefour guide lines of the guide base runs at all times to the surface. Theconductor casing string, the guide base and the guide lines are thenlowered down towards the seabed where the conductor casing string isguided into the lead hole, so that the guide base eventually is placedin an upper sedimentary layer in the seabed, and where this layer isnormally made up of loosely composed and finely grained sedimentaryparticles as well as water, a mixture often referred to as mud. In thisconnection the lead base must be placed as vertically as possible downinto the seabed.

After the location of the guide base on and in the seabed and after thecementing of the conductor casing string in the pilot hole has beendone, one may, if desired, lower down a drill string, a casing string, ariser string or other necessary equipment, as such equipment is guidedinto position at the well centre line by means of the above guide lines,connected to the guide base.

As an alternative to the guide base's above guide lines, the guide basemay be equipped with a funnel shaped sleeve, which is not described ingreater detail, but in which such a sleeve has proved to be moresuitable when working with wells at great sea depths.

In the use of known technique a guide base does not function as a loadcarrying construction in the founding of the well. Such loads typicallyconsist of both pressure and torsion forces created by the weight of ablow out valve, well heads, casing strings in the well and other relatedequipment, as well as lateral forces caused to the blow out valve and/orthe riser string by ocean streams, or as a result of the drift of afloating drilling installation. These loads are taken up by theconductor casing string, which therefore must be dimensionedaccordingly, to avoid bending and breaking.

DISADVANTAGE OF KNOWN TECHNIQUE

The known substructure devices are encumbered with some disadvantagesconcerning strength and costs.

The drilling of a pilot hole as described above, and in which thedrilling is done in loosely composed and substantially water filledwaterbed sediments, often leads to great washouts of the wall of thepilot hole, and the greatest washouts often take place in the upper partof the lead hole.

By subsequent cementing of the conductor casing string, one will oftenachieve an unsatisfactory filling of cement grout in the expandedtubular space between the wall of the conductor casing string and thepilot hole. After the cement grout is hardened in the tubular space,this may lead to the load carrying conductor casing string getting anunsatisfactory lateral support for the above loads. Moreover, thehardened cement grout acts as a safety pressure barrier for possibleoutflows of e.g. gas in underlying shallow layers of the baseformations, and an unsatisfactory cementing can weaken or eliminate thispressure barrier. In addition, large amounts of cement grout arerequired for the cementing of a conductor casing string, and the volumeincreases according to the degree of washing out that has taken placeduring the drilling of the pilot hole.

The method of first drilling a pilot hole, for then to cement aconductor casing string, may also lead to an unfortunate or unacceptablevertical deviation on the installed conductor casing string, either dueto the pilot hole being drilled obliquely down into the seabed, orbecause the conductor casing string is not kept sufficiently immobilewithin an acceptable vertical deviation during the time needed for thecement grout to develop sufficient rigidity for supporting the conductorcasing string. The drilling of pilot holes and the following cementingof the conductor casing string is further complicated when in deep waterlocations. This has to do with both the conductor casing string beingaffected by ocean streams and as a consequence of possible drift of afloating drilling installation, but also as a consequence of low seabedtemperatures, which may lead to an extremely long hardening period forthe cement grout.

The method of first drilling a pilot hole for then to cement a conductorcasing string is in this context the main problem, and this method is inaddition time consuming and expensive as the work i.a. must be performedwith a drilling rig.

SUMMARY OF THE INVENTION

The present invention makes available a substructure device in the shapeof a suction substructure having the necessary capacities andconstructive features making it possible to pre-install the suctionsubstructure, and at least one conductor casing string, using other andpossibly smaller vessels than the present installation vessels, i.e. asuitable boat, and by piling technique. Thus, most of the abovementioned disadvantages are reduced or avoided.

How the Object is Achieved

According to the invention suction substructure is used prior to theinstallation of one or more conductor casing strings for the drilling ofone or more underwater wells, preferably petroleum wells. The suctionsubstructure and the conductor casing string(s) is/are installed from aninstallation device or installation vessel, e.g. a suitable boat,located on the surface, hereinafter only referred to as installationvessel.

The suction substructure is made up of e.g. a cylinder shapedsubstructure body whose shape has features resembling a cup or a glass,and which consist of an encompassing vertical part, or mantle, and wherethe substructure body at one end consists of an open part, which part inthe operating position constitutes the bottom of the substructure body,and where the substructure body in the other and upper end, with theexception of a preferably circular opening, preferably consists of aclosed horizontal part, e.g. a horizontal lid part, and where thesubstructure body otherwise is joined in a pressure sealing manner, e.g.by welding.

The above mentioned opening in the horizontal part, hereinafter referredto as guide opening, is surrounded by a conical guide funnel, joined tothe substructure body in a pressure sealing manner, e.g. by welding,being external and overlying, preferably circular, having its maximumdiameter in the upper end part. Thus, when applied on the seabed theguide funnel is suited to receive and centre a conductor casing stringto have it forwarded into the suction substructure and down into theseabed sediments. The guide funnel may be shaped with an outer part, inrelation to the substructure body, and a co-operating inner part,respectively an outer and upper guide funnel part as well as an innerand lower guide funnel part, and where the two guide funnel parts arepreferably shaped in an interconnected fashion in the substructure body.The lower guide funnel part may alternatively be shaped with a continuedcone in relation to the upper guide funnel part, so that the outletdiameter of the lower guide funnel part at the bottom end constitutesthe smallest or largest diameter of the guide funnel, or where the lowerguide funnel part is tubular with a constant diameter, or where thisguide funnel part is shaped in another suitable way with regard to theactual conditions, e.g. ocean depths, with which one is working.

Alternatively, it is possible to fit the suction substructure withseveral guide funnels, and in which the shape of the suctionsubstructure must be adapted to the number of guide funnels and theirmutual positions, and in which the suction substructure, seen in planedrawing, may be given a rectangular or other non-circular shape. Thismay be opportune in the setting of more conductor casing strings, socalled batch setting, e.g. in connection with the drilling of a numberof production or/and injection wells in an oil field.

Besides, the inner part of the substructure body will due to strengthand possibly construction considerations have to be fitted withpartitioning walls.

In the installation of the suction substructure the upper end part ofthe guide funnel, or, possibly, the upper end parts of the guidefunnels, must be fitted with a lid or a similar device which isreleasable and pressure sealing, e.g. by way of suitable washers lid orthe like. A lid is attached to the upper end part of the guide funnel bymeans of a releasable fastening device, e.g. a screwing or clampingdevice, and where the releasable fastening device preferably is releasedby the use of a remotely operated submarine vessel (“ROV”).

The lid, or at least one of the lids, must also be fitted with a throughbore in which an outlet pipe or a suitable outlet hose is connected tothe outer side of the suction substructure, and where the outletpipe/outlet hose on this outer side is connected to a pump. Thelid/lids, the outlet pipe/outlet hose and the pump must otherwise bearranged to the substructure body e.g. by means of flanges, couplings,valves, seals or other necessary devices or equipment. In the case wherethe guide funnel as mentioned above is shaped with one outer and upperguide funnel part, as well as one inner and lower guide funnel part,which in operating position runs totally, or almost totally, to the openbottom part of the substructure body, and where the two guide funnelparts in addition are joined in a continuous and pressure sealing mannerto the substructure body, one may in an upper part of the enclosingvertical part or upper horizontal part of the substructure body, butoutside the guide funnel parts, equip the substructure body with athrough bore in which an outlet pipe or a suitable outlet hose isconnected on the outer side of the suction substructure, and where theoutlet pipe or the outlet hose on this outer side is connected to apump.

When in use, the installation vessel lowers the substructure body downto the chosen location on the seabed, e.g. by means of a suitableinstallation line which may be connected to a suitable number of liftingdevices or similar fastening devices on the substructure body and via asuitable releasable lifting device or similar lifting device. When thesubstructure body thus is brought into contact with the seabedsediments, and where these normally appear in the shape of mud, thesubstructure body's downwards open end part is by virtue of thesubstructure body's own weight pressed some way down into the soft andwater filled seabed sediments. Simultaneously and later in theinstallation process an adjusted vertical and upwards pressure ismaintained in the installation line, so that the substructure body iskept in a nearly vertical position and within a given vertical tolerancedeviation. The maintenance of the desired vertical position of thesubstructure body may e.g. be monitored by a remotely operated submarinevessel. By preference the same vessel is then connected to the abovementioned pump, as the vessel is fitted with the necessary connectiondevices, equipment and remedies for carrying out this and the subsequenttasks. From this vessel the pump is then activated in such a way thatthe water located inside the substructure body is pumped out, or suckedout of the substructure body, and thus the name suction substructurefollows. This pumping out of water leads to the creation of a lowerpressure inside the substructure body, in relation to the surroundingwater and its hydrostatic pressure, and to the substructure body thusbeing pressed down into the mud, so that the substructure body isanchored to and in the seabed. It may be necessary in this connection tomake the installation process in several steps, and in which theremotely operated submarine vessel during the installation is used forcontrolling that the suction substructure, which may be fitted with therequired visual measuring equipment, is pressed as vertically aspossible down into the seabed and within the desired vertical settingclearance for the substructure, and that the substructure is pressedadequately deep into the seabed sediments. Prior to the installation ofthe suction substructure one has preferably collected seabed sedimentsamples, so that one may determine the necessary penetration depth ofthe substructure body in the seabed sediments.

Then, possibly, the releasable and pressure sealing lid/lids from theguide funnel(s) of the suction substructure are coupled, so that theguide funnel(s) then are open for the later installation of guide pipes.In the following description it will, for the sake of simplicity, bereferred to a suction substructure with only one guide funnel.

A conductor casing string is then lowered down from the installationvessel on the surface to the suction substructure and its guide funnel.During the lowering, the conductor casing string is guided towards andto the guide funnel of the suction substructure, preferably by means ofthe dynamic positioning device(s) of the installation vessel inco-operation with a submarine vessel, which performs visual underwaterobservations of the conductor casing string's position in relation tothe suction substructure. If suitable, and in accordance with knowntechnique, the conductor casing string may be guided towards and to theguide funnel of the suction substructure by means of guidelines, whichare adapted and fastened to the suction substructure. The lower part ofthe conductor casing string is called a conductor casing string shoe, inwhich one in this connection preferably has mounted a piling hammer anda piling spear. The conductor casing string shoe, the piling hammer andthe piling spear are positioned vertically above, and are then insertedinto the mentioned guide funnel until the piling spear is brought intocontact with the seabed, whereupon the piling spear as a consequence ofthe conductor casing string's own weight penetrates down into the seabedmud, so called autopenetration. In this way the conductor casing stringis kept in place and the required lateral support and stability issecured in this position. To achieve the best possible vertical steeringof the conductor casing string through the suction substructure, aconstant outer diameter of the conductor casing string is sought, sothat the smallest diameter of the guide funnel must exceed the conductorcasing string's outer diameter to a sufficient degree, so that theconductor casing string during installation may pass freely through theguide funnel, but where the smallest diameter of the guide funnel at thesame time is sufficiently small to be able to give the conductor casingstring the required lateral support during installation and piling, aswell as the necessary lateral support of the conductor casing string bylater use of it as anchoring point for e.g. a wellhead.

The installation of a suction substructure according to the inventionrenders possible a conductor casing installation by means of knownpiling technique. In connection with the coupling of the conductorcasings, and before the conductor casing string is lowered down to thesuction substructure, one on the conductor casing shoe internallyeffective and e.g. hydraulically activated piling hammer is installed inthe conductor casing string, which also is equipped with necessarycontrol hoses, power supply hoses and other equipment necessary in thisconnection. After the conductor casing string thus, as described above,is guided into place in the suction substructure and the conductorcasing shoe has penetrated the upper layer of the sea bed mud, theconductor casing string is driven by means of the describedhydraulically activated pile hammer down into the seabed sediments tothe desired depth, and so that the upper end of the conductor casingstring extends sufficiently over the suction substructure, upon whichthe pile hammer is disconnected and lifted to the surface together withthe accompanying hoses and equipment. If the upper end of the conductorcasing string extends too much over the seabed, one may by means of aremotely operated submarine vessel cut the surplus length of theconductor casing to the desired length over the suction substructure,and the surplus pipe length may then be hoisted up to the installationvessel.

By means of the suction substructure and the method for installing it onand in a seabed, one has rendered possible installation of conductorcasing down to an optimal setting depth, at the same time as the seabedsediments, which due to the piling surround the conductor casing, hasbecome somewhat compressed, and where the conductor casings thereafterdo not contain loose sediments or other obstacles, e.g. rests of cementgrout, and where the conductor casing string extends with a desiredlength over the suction substructure, in which the surplus length isoptimally adapted to the specific well requirements.

Advantages

By using the present invention one achieves being able to use knownpiling technique for driving the conductor casing string(s)approximately vertically down into the seabed, which may be performed byusing a smaller installation vessel than e.g. a drilling rig, which istypically used in known conductor casing installation.

The installation of a suction substructure in combination with piling ofconductor casing is remarkable due to the fact that this combination inrelation to known conductor casing installation has a good ability toabsorb the horizontally and vertically effective forces/loads asdescribed above, and where the suction substructure as opposed to knownguide frame installation also contributes to the absorption of suchforces/loads.

The piling of conductor casing, as opposed to the drilling of holes andthe subsequent cementing of the conductor casing, also leads to minimaldisturbances to the seabed sediments which have been penetrated in thepiling, leading to optimal collusion between seabed sediments andconductor casing. Such an installation also prevents the washing out ofseabed sediments under the substructure during the subsequent throughdrilling of the installed conductor casing string. Such a washing out isa usual problem in the use of known technique for installation ofconductor casing. Moreover, it will not be necessary in the piling ofconductor casing(s) to cement the conductor casing string(s) after thepiling of it/these has/have been performed.

In addition to the advantages in construction, one may through thepre-installation of conductor casing according to the invention achieveconsiderable economic benefits, as one as described may use other andsmaller installation vessels than e.g. a drilling rig, and where onesimultaneously achieves a more attractive conductor casing installation,seen from a security point of view. As a consequence of the piling ofthe conductor casing string(s) and the fact that the conductor casingstring(s) in this way receives better lateral support, it will now bepossible to have part of the horizontal forces loads, which in knowntechnique are absorbed by the conductor casings, absorbed by the seabedsediments. Thus, as a consequence of the use of the suctionsubstructure, one may dimension the conductor casing for lesser torsionand breaking loads, and thus apply smaller conductor casing dimensions,which also reduces the conductor casing costs in the drilling of anunderwater well.

The use of the present invention, in which the conductor casing stringextends with a desired surplus length over the suction substructure alsorenders possible an installation which is secure in terms of strengthand suitable, of a wellhead on the mentioned conductor casing string, inthat the well head in relation to known installation technique may beinstalled in greater distance over the seabed. This means i.a. easieraccess for an underwater vessel to the suction substructure and e.g. awellhead, but as well that drilled out drill hole fragments, orcuttings, are not gathered in an unwanted height over the seabed aroundthe suction substructure, thus creating operating problems, by the factthat one in an early phase of the drilling of the well dumps thecuttings on the seabed around the substructure.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following part of the description, it will be referred todifferent and not-limited executions of the invention, with reference tothe FIGS. 1-5, in which one certain number of reference refers to thesame detail in all drawings where this detail occurs, and where:

FIG. 1 shows a perspective view of a cylinder shaped suctionsubstructure, in which the upper end of the suction substructure isshaped with a horizontal part being equipped with one around the centreline of the substructure body positioned circular guide openingsurrounded by an outer cylindrically shaped and conical guide funnel,having its largest diameter in the upper end part, and where thecylinder shaped substructure body otherwise is joined together in apressure sealing manner, e.g. by welding;

FIG. 2 shows a view in perspective of the same suction substructure asshown in FIG. 1, but where the guide funnel is shaped having an upperand outer guide funnel part and a lower and inner guide funnel part, andwhere the two guide funnel parts are jointly shaped centrally in thesubstructure body. The lower guide funnel part is shaped with an inrelation to the upper guide funnel part extended cone, so that theoutlet diameter of the lower guide funnel part constitutes the smallestdiameter of the guide funnel;

FIG. 3 shows a perspective view of the suction substructure according toFIG. 1, in which the lower open part of the substructure body is beingpressed down into the seabed sediments;

FIG. 4 shows a view in perspective of a suction substructure accordingto FIG. 1, but where the substructure is shown fully installed on and inthe seabed, and where a section of the lower part of a conductor casingstring is shown positioned in the guide funnel of the suctionsubstructure and in the seabed sediments, as the conductor casing stringis being piled down into the seabed; and where

FIG. 5 shows a view in perspective of the suction substructure accordingto FIG. 1 and FIG. 4 and where the suction substructure is shown afterinstallation in and on the seabed, but where the vertical part/mantle ofthe suction substructure, as opposed to in FIG. 4, is positioned with asubstantial vertical deviation on and in the seabed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Equipment and/or arrangement which do not directly apply to theinvention itself, but which still are necessary prerequisites for theoperation of the invention are not more closely defined or described indetail in the following operating examples. Such equipment and/orarrangement includes e.g. surface vessels, submarine vessels, hoistingequipment, guide lines, pipes and hoses, couplings, valves, pumps,control equipment and possibly other necessary equipment or devices.This is well-known equipment for a person qualified in the field.

FIG. 1 and FIG. 2 show a suction substructure 2 formed of a cylindershaped and encompassing vertical part/mantle 4 being joined in apressure sealing manner, e.g. by welding, having an upper circularhorizontal part/lid part 6, and where the suction substructure 2 isshaped with one in the operating position open end part 8 in the lowerend of the suction substructure 2. The lid part 6 is shaped with athrough-going guide opening 10, to which guide opening 10 an outer andpreferably circular guide funnel 12, hereinafter referred to as an outerand upper guide funnel part 12, is formed in a pressure sealing manner,e.g. by welding. The intention of the guide funnel 12 is i.a. tofacilitate the introduction of a conductor casing string 14 in thesuction substructure 2, but the guide funnel 12 is also equipped tosupply lateral support and direction stability in the subsequent pilingof the conductor casing string 14. In all the drawing figures thesuction substructure 2 is externally equipped with three lifting airs16. In the same way an inner part of the suction substructure is forreasons of strength in this example equipped with three supporting walls18 (FIG. 1) and 18′ (FIG. 2), radially positioned in relation to thecentre line of the suction substructure 2. The suction substructure 2according to FIG. 2 is externally identical to the suction substructure2 according to FIG. 1. In FIG. 2 the suction substructure 2 is inaddition fitted with an inner and lower guide funnel part 20, as theguide funnel parts 12 and 20 are continuously arranged to the suctionsubstructure 2. The lower guide funnel part 20 is conical, so that thediameter of the lower guide funnel part 20 in the lowest lying positionof the operating position constitutes the smallest diameter of the guidefunnel part 20. Such a shape may e.g. be well suited for conditionsrequiring a lengthier support (stiffening) of the guide pipe.

In FIG. 3 the suction substructure 2 according to FIG. 1 is about to bepressed down into soft and water filled sediments 22 under a slopingseabed 24, having overlying seawater 26. In this situation the suctionsubstructure 2 is connected to a surface vessel, not shown in thedrawings, by means of an installation line 28 and a lower three armedlifting straddles 30 which is connected to the lifting ears 16 of thesuction substructure 2. The guide funnel 12 of the suction substructure2 is closed in the upper open end with a releasable lid 32, which ispressure sealing around its circumference, said lid 32 is fitted with athrough outlet pipe 34 which is coupled to an external pump 36. The lid32 is arranged to the guide funnel 12 in a pressure sealing manner bymeans of washers, not shown in the drawings, situated between the lid 32and the guide funnel 12. The lid 32 is also fitted to the guide funnelby means of a releasable fastening device, not shown in the drawings,e.g. a screwing or clamping device, and where the releasable fasteningdevice preferably is removed by a remotely operated underwater vessel,not shown in the drawings. After the suction substructure 2 has beenlowered from the surface vessel and via the installation line 28 and thelifting straddle 30 down to, and as a consequence of the net weight ofthe suction substructure 2 has been partly pressed down into thesediments 22 under the waterbed 24, a certain tension is maintained inthe installation line 28. The direction for the tension force isindicated in FIG. 3 by an upwards pointing arrow. At the same time oneuses e.g. a remotely operated underwater vessel, not shown in thedrawings, which is guided to and coupled to the pump 36, whereuponsuited equipment on the underwater vessel runs the pump 36 so thatseawater 26 is pumped out of the suction substructure 2. The outletdirection of the seawater 26 is indicated in FIG. 3 and by the pump 36by a horizontal arrow. The mentioned pumping out of seawater 26 causesthe internal fluid pressure of the suction substructure 2 to be lowered,so that a pressure differential between this pressure and thehydrostatic pressure of the seawater 26 surrounding the suctionsubstructure 2, so that the suction substructure 2 thus is supplied witha downwards pressure force pressing the suction substructure 2 down intothe seabed sediments 22. The direction of this pressure force isindicated in FIG. 3 by an arrow pointing downwards. To be able toinstall the suction substructure 2 as vertical as possible and on and inthe seabed 24, a vertically upwards tension force is maintained in theinstallation line 28, being inferior to the downwards pressure force.The suction substructure 2 will in practice be fitted with suitablemeasuring equipment, not shown in the drawings, by which the verticalposition of the suction substructure 2 may be checked, e.g. by means ofa remotely operated underwater vessel, and where a vertical adjustmentof the suction substructure 2 is performed by the mutual adaptation,possibly by steps, of the above mentioned forces in relation to eachother, so that the suction substructure 2 is left standing in anapproximately vertical position on and in the seabed 24.

As shown in FIG. 4, and after the completed installation of the suctionsubstructure 2, the conductor casing string 14 is lowered, preferably bymeans of accurate positioning of the installation vessel, combined withthe visual observation of the underwater vessel, down and through theguide funnel 12, so that the conductor casing string 14 is brought intocontact with one, in the example, sloping seabed 24, and thereafter, asa consequence of its own weight is pressed some way down into the seabedsediments 22 and is left standing in an approximately vertical positiontherein. Then, one uses, according to known technique, e.g. anhydraulically operated piling hammer, not shown in the drawings, forramming the conductor casing string 14 further down to a planned depthin the seabed sediments 22. The installation of the conductor casingstring 14 by means of piling is rendered more efficient by the use of apiling hammer, not shown in the drawings, with a piling spear, in thelower end of the conductor casing string 14, or in the conductor casingshoe 38 of the conductor casing string 14, as the piling spear 40 leadsto a reduction of the penetration resistance between the conductorcasing string 14 and the seabed sediments 22.

FIG. 5 shows, in relation to FIG. 3 and FIG. 4 the same installation ofthe suction substructure 2 and the conductor casing string 14 on and ina sloping seabed 24, but where the vertical part/mantle 4 of the suctionsubstructure (2) in FIG. 5 is shown arranged in the operating positionhaving a substantial vertical deviation in relation to the suctionsubstructure shown in FIG. 4. Such a vertical deviation may e.g. occurdue to a sloping seabed 24 and/or e.g. as a consequence of the fact thatthe sediments 22, of which the seabed consists, not having a uniformconsistency in relation to each other, a fact that may cause unevenpressing-in of the suction substructure 2. The resulting verticaldeviation does still not prevent vertical introduction of the conductorcasing string 14 through the guide funnel 12, and that the conductorcasing string 14 thereupon may be piled further down into the seabedsediments 22.

What is claimed is:
 1. A method for piling a conductor casing string(14) into sediments (22) of a waterbed (24) by using a floatinginstallation vessel, the installation vessel being provided with meansfor practicing said method, said means including hoisting equipment,cables, conduits for power supply and equipment control, connections andfittings, valves, pumping means and control equipment, said pilingmethod requiring that the interior of the conductor casing string (14),at the lower end and casing shoe (38) thereof, be provided with areleasable piling hammer, and a cooperating piling spear (40), saidconductor casing shoe (38) and piling spear (40) also being providedwith force-transmitting striking surfaces, onto which surfaces saidpiling hammer repeatedly exerts its impact force and drives theconductor casing string (14) into the waterbed (24) during the pilingoperation, wherein the method is initiated by lowering into water (26)from said floating installation vessel a suction substructure (2) whichis installed onto and within the sediments (22) of the waterbed (24),the suction substructure (2) providing necessary and stabilizing lateralsupport for the conductor casing string (14) during its installation inthe sediments (22), hence making possible to install by means of pilingthe upper end of the conductor casing string (14) as vertical aspossible, and within a small vertical tolerance, within said sediments(22) of the waterbed (24), and wherein the suction substructure (2), inorder to achieve said verticality, is provided with a supporting mantle(4), an upper lid part (6) and a downwards open part (8) which, due tothe weight of the suction substructure (2), is pressed some distanceinto the sediments (22) when being lowered therein, the lid part (6)being provided with at least one through-going guide opening (10) whichupon said lowering is connected in a pressure sealing manner to anassociated, releasable lid (32), the suction substructure (2) also beingprovided with an outlet conduit (34) connected to a pump (36) which thenis activated and pumps the water (26) out of the suction substructure(2), thus pressing the suction substructure (2) further into thesediments (22) of the waterbed (24), whereupon the releasable lid (32)is removed from the guide opening (10) or, alternatively, from at leastone guide opening (10), the suction substructure (2) thus being preparedfor the subsequent piling of the conductor casing string (14),characterized in that the method comprises, in sequence, the followingsteps: a) lowering the conductor casing string (14) containing thepiling hammer and the cooperating piling spear (40) into water (26) anddown to the suction substructure (2), the conductor casing string (14)being lowered on an installation line (28) connected to the floatinginstallation vessel; b) guiding, while hanging down from theinstallation line (28), the piling spear (40) and a lower part of theconductor casing string (14) through the guide opening (10) in thesuction substructure (2), and then lowering them down towards thesediments (22) and, due to the weight of the conductor casing string(14), pressing them some distance into said sediments (22), the guideopening (10) thereby providing said stabilizing lateral support for theconductor casing string (14) during its installation in the sediments(22) of the waterbed (24); c) initiating the piling of the conductorcasing string (14) by supplying the piling hammer with necessary motivepower through a conduit from the floating installation vessel, thepiling hammer thereby driving the piling spear (40) and the conductorcasing string (14) down to a desired depth within the sediments (22),the entire piled length of conductor casing string (14) thereinafteradhering to the surrounding sediments (22), hence providing theconductor casing string (14) with optimum lateral stabilizing supportand associated optimum load-supporting properties, the suctionsubstructure (2), when in position of use, also providing the conductorcasing string (14) with an upper anchoring or clamping point whichsubstantially increases the load-carrying capacity of the conductorcasing string (14) with respect to bending and buckling caused bysubsequent well loads exerted onto the conductor casing string (14),including the weight of a wellhead and a blowout preventer; and d)disconnecting and removing downhole piling equipment, including thepiling hammer and the piling spear (40), from the conductor casingstring (14), thus completing the installation of the conductor casingstring (14) in the sediments (22) of the waterbed (24), hence enablingsubsequent drilling of an underwater well to be initiated through thepiled conductor casing string (14).
 2. A method according to claim 1,further characterized in step c) as driving the piling spear (40) andthe conductor casing string (14) down to a depth within the sediments(22) which allows an upper end portion of the conductor casing string(14) to project above the suction substructure (2) on the waterbed (24),thus allowing the wellhead and/or the blowout preventer to be mounted ontop of the conductor casing string (14).
 3. A method for piling anelongated conductor casing string into a bed of sediments lying underwater, the method comprising the steps of: lowering a suctionsubstructure into the water and onto the sediments, the suctionsubstructure comprising a supporting mantle, an upper lid part and adownward open part, the downward open part being forced into thesediments by the weight of the suction substructure, the upper lid partprovided with at least one through-going guide opening which uponlowering is connected in a pressure sealing manner to a releasable lid,the suction substructure further comprising an outlet conduit connectedto a pump; activating the pump to pump water from the suctionsubstructure, thereby creating a suction force that forces the suctionsubstructure further into the sediments; removing the releasable lidfrom the at least one through-going guide opening; lowering theelongated conductor casing string into the water and down to the suctionsubstructure; guiding a lower end of the elongated conductor casingstring through the guide opening and into the sediments, wherein theguide opening provides stabilizing lateral support for the elongatedconductor casing string; and piling the conductor casing string to adesired depth into the sediments.
 4. The method of claim 3, wherein, asa result of the piling, the entire length of the elongated conductorcasing string adheres to the sediments, thereby providing the elongatedconductor casing string with optimum lateral stabilizing support andassociated optimum load-supporting properties.
 5. The method of claim 3,wherein, as a result of the guiding of the conductor casing string, thesuction substructure provides the elongated conductor casing string withan upper anchoring or clamping point which increases the load carryingcapacity of the conductor casing string with respect to bending andbuckling caused by subsequent well loads exerted onto the conductorcasing string, the well loads comprising the weight of a wellhead and ablowout preventer.
 6. The method of claim 3, wherein the lower end ofthe elongated conductor casing string comprises a piling spear forpiling the conductor casing string into the sediments.
 7. The method ofclaim 6, wherein the piling spear and the elongated conductor casingstring are piled down to the desired depth within the sediments by apiling hammer through a conduit from an installation vessel.
 8. Themethod of claim 7 further comprising the step of: uncoupling andremoving the piling hammer and piling spear from the elongated conductorcasing string, thus completing the installation of the elongatedconductor casing string in the sediments and enabling subsequentdrilling of an underwater well to be initiated through the installedelongated conductor casing string.
 9. The method of claim 3, whereinafter piling the elongated conductor casing string into the sediments,an upper end of the elongated conductor casing string projects above thesuction substrate, thus allowing a well head or blowout preventer to bemounted to an upper end of the elongated conductor casing string.